The present invention relates to a gas discharge closing switch and, more particularly, to a multiple surface high voltage structure for such a switch.
Gas discharge closing switches, such as thyratrons, are used for rapid switching of high voltage, high current signals with low power consumption. A typical thyratron has an anode connected to high voltage and a cathode held at ground potential. A control electrode or "grid" is placed between the anode and the cathode. Upon application of a positive control pulse, the control electrode closes the switch by drawing electrons from the cathode to transform gas within a housing or "envelope" of the device into a dense, conducting plasma.
In certain applications, particularly when thyratrons are used to switch pulsed high power lasers, very high currents must be switched in very short periods. Additionally, the lumped element transmission line circuits of pulsed laser systems often are characterized by mismatches that create high inverse voltage swings between the anode and the cathode. In thyratrons of conventional design, extreme inverse voltages can drive gaseous ions against the anode, thereby sputtering anode material and forming arc spots on the surface of the anode.
Attempts have been made to mitigate anode damage by providing a thyratron with an anode capable of functioning as a cathode under inverse voltage conditions. This causes current to flow opposite to the direction of normal (forward) conduction, thereby reducing the inverse voltage by means of a nondestructive glow mode. A structure of this type is disclosed in UK Patent No. 1,334,527, in which an anode is heated and contains emitter material.
Another proposed approach is to construct an anode as a hollow box having an aperture through which plasma can pass when the device operates, as disclosed in U.S. Pat. No. 4,517,090. The anode of the '090 patent is designed to store plasma within its interior during forward conduction to support current flow in a reverse direction when exposed to an inverse potential.
Although the foregoing devices reduce anode damage, they also constrain anode design. Therefore, it is desirable in many applications to provide a thyratron which permits reverse conduction without unduly restricting the shape, size and composition of its anode. In addition, it is desirable to provide a device in which plasma is stored at a plurality of locations along an anode surface to facilitate reverse conduction.